1. Field of Invention
The present invention relates to a toner for image formation, a method of producing the toner, a toner container, a toner cartridge, and a process cartridge for containing the toner therein, and an image forming apparatus to which such a toner container, toner cartridge or process cartridge is detachably attached.
2. Discussion of the Background
Electrophotographic image formation can be carried out by various methods, but it is generally carried out by forming a latent electrostatic image on the surface of a photoconductor which is prepared by use of a photoconductive material, developing the latent electrostatic image to a visible toner image with a developer, and when necessary, transferring the toner image to a transfer sheet such as a sheet of paper, and fixing the transferred toner image to the transfer sheet with application of heat and/or pressure, or by the application of the vapor of a solvent thereto, as described in, for instance, U.S. Pat. No. 2,297,691, JP-B-49-23910, and JP-B-43-24748.
Methods of developing latent electrostatic images to visible toner images can be broadly divided into two groups. One is of a liquid development type, which uses a liquid developer composed of various kinds of pigments and/or dyes, which are finely divided and dispersed in an electrically insulating organic solvent, and the other is of a dry development type, which uses a dry developer (hereinafter referred to as toner) which can be prepared by dispersing a coloring agent such as carbon black in a natural or synthetic resin. In the dry type development, for instance, a cascade method and a magnetic brush method can be employed for developing latent electrostatic images formed on the photo conductor.
In recent years, the dry type development is widely used.
In the dry type development, a heat roller is generally used for fixing toner images on the transfer sheet due to the excellent heat transfer efficiency of the heat roller.
In recent years, for energy saving, there is a growing tendency to reduce the amount of energy to be applied to the toner for fixing thereof.
In 1999, a technical research project concerning copying machines for the next generation in DMS (Demand-Side Management) Program of IEA (International Energy Association) announced the specifications for copiers with a copying speed of 30 cpm or more to the effect that it is required that the waiting time for starting image fixing be within 10 seconds, and the power consumption during the waiting time be in the range of 10 to 30 watt, although the power consumption differs depending upon copying speed. The energy saving required to be achieved in the specifications is significantly greater than that achieved in the currently employed copying machines.
As a method for meeting the above requirement, there may be a method of reducing the heat capacity of an image fixing member such as an image fixing roller, thereby increasing the temperature response of the image fixing member to the toner heated. However, this method cannot sufficiently meet the requirement.
For minimizing the waiting time to meet the above requirement, the lowering of the image fixing temperature of the toner itself is considered to be technically essential.
In order to achieve the low-temperature image fixing, a polyester resin, which has excellent low-temperature image fixing performance and relatively good heat resistance and thermal preservability, has been tested instead of the styrene-acrylic resin which has conventionally used in many cases as disclosed in JP-A-60-90344, JP-A-64-15755, JP-A-2-82267, JP-A-3-229264, JPA-3-41470, and JP-A-11-305486.
Furthermore, it was tried that a particular non-olefinic crystalline polymer was added to a binder in order to improve the low-temperature image fixing performance as disclosed in JP-A-62-63940.
Furthermore, it was tried that a crystalline polyester was used as disclosed in Japanese Patent No. 2931899. However, no optimization has not yet been made with respect to the molecular structure and molecular weight thereof.
Even if the above-mentioned prior is used, it is still impossible to meet the requirements described in the specifications of DMS (Demand-Side Management) Program. In order to meet the requirements, the establishment of a further more advanced low-temperature image fixing technology than the conventional one is indispensable.
In order to attain a further lower temperature image fixing, it is necessary to control the thermal characteristics of the resin itself to be used. However, if the glass transition temperature (Tg) of the resin is excessively lowered, the heat resistance and thermal preservability of the toner are impaired. When the softening point F1/2 of the resin is lowered by use of a resin with a smaller molecular weight, problems such as the lowering of the hot-offset occurring temperature are caused. For these reasons, the obtaining a toner having excellent low-temperature image-fixing performance and high hot-offset occurring temperature has not been obtained by controlling the thermal characteristics of the resin itself.
In order to eliminate these shortcomings, there has been proposed a technique of using a polyester resin as a binder resin and preparing toner particles in water by utilizing an isocyanate reaction as disclosed in JP-A-11-149180. However, it cannot be said that the low-temperature image fixing can be sufficiently achieved. Furthermore, it is difficult to apply this method to a negative toner, since the toner becomes positively chargeable due to the formation of a urea group by the isocyanate-amine reaction.